Navigation system



DeC- 25, 1962 L. R. CHAPMAN, JR 3,070,331

NAVIGATION SYSTEM Filed March 18, 1955 2 Sheets-Sheet 1 @fm f lrl l i 05756702 l l l 7z 7 INVENTOR.

'Z 5 wz/f a. [fw/mu 3,070,331 NAVIGATIN SYSTEM Leslie R. Chapman, Jr., Thoma/ood, NY., assigner to General Precision, Inc., a corporation of Delaware Filed Mar. 18, 1955, Ser. No. 495,081 12 Claims. (Cl. 244-77) This invention relates to a navigation system and particularly to an airborne navigation system for guiding an unmanned aircraft along a predetermined path for a predetermined distance.

The art of aerial navigation by means of airborne apparatus entirely independent of ground based stations has received considerable attention in recent years. Various approaches to the problem have been proposed but at the present time, systems employing Doppler radar techniques are the most highly developed. ln a typical Doppler radar navigation system, two beams of microwave energy, making a iixed angle with respect to each other in the horizontal plane, `but rotatable together about a vertical axis, are directed from the aircraft toward the earth at equal vertical angles. The reected energy received from each beam will be shifted in frequency from the transmitted energy due to the relative motion between the aircraft and the earth. lf the beams make unequal angles (in the horizontal plane) with the ground track of the aircraft, the two received frequencies will be shifted -unequally. The difference in the received frequencies is used as an error signal to rotate the beams about a vertical axis until the two received frequencies are equal. Then the bisector of the angle between the beams represents the ground track of the aircraft and the angle between this bisector and the longitudinal axis of the aircraft is the drift angle, a. The frequency shift is proportional to ground speed, Vg.

Many navigation systems have been built around Doppier radar systems to enable an aircraft to be guided to any point on the surface of the earth. rthese systems are usually complex, involving gyroscopic and magnetic elements to obtain an accurate heading reference, computers for calculating the great circle course between any two points, corrections for the ellipticity of the earth, and many other refinements. Such systems are obviously too complex to be suited for use in a pilotless craft which maires but one ilight. Considering the other extreme, a missile containing no navigational equipment whatsoever could be launched with the proper initial course but the probability of its `striking a preselected target decreases rapidly with distance.

it is an object of this invention to provide a completely airborne navigation system suitable for use in a pilotle-ss craft.

Another object of the invention is to provide apparatus for guiding an aircraft over a predetermined ground path.

Another object of the invention is to provide apparatus for guiding an aircraft along a predetermined course for a predetermined distance.

Another object of the invention is to provide a completely airborne navigation system for gliding an aircraft over a predetermined ground path without requiring the determination on the craft of either true or magnetic north.

The invention comprises apparatus, such as a Doppler radar system, for measuring continuously the ground speed and the drift angle of the craft. Also included is a gyroscope for measuring continuously the angle between the desired course and the axis of the craft. in one embodiment, the dilference between the latter angle and the drift angie is lused as an error signal to steer the craft.

round speed is integrated to obtain distance travelled, and after a preselected distance has been traversed, a sig- States L ate t ice nal is generated to cut off the propulsion mechanism or to steer the craft downward, or both.

For a clearer understanding of the invention, reference may be made to the accompanying drawing in which:

FIGURE l is a block diagram of one embodiment of the invention;

FIGURE 2 is a diagram useful in explaining the invention;

FGURES 3 and 4 illustrate various lforms which the integrator of FIG. l may take;

FIGURE 5 is a diagram useful in explaining a modilication of the invention; and

FIGURE 6 is a block diagram of a modified forni of the invention.

Referring now to FIG. l, there is shown a Doppler radar system l1. The details of this system are not a part of the present invention and it may take many forms, it only being required that the system determine continuously the horizontal component of ground speed Vg and the drift angle of the aircraft. T he system may, for exam-ple, be similar to that described in the copending application of Tull and Gillette, Serial No. 749,184, filed May 20, 1947, for Navigation System, now Patent No. 2,869,118 granted January 13, 1959, or to that described in the copending application of Berger and Tull, Serial No. 49,926, filed September 18, 1948 for Course and Speed lndicating System, now Patent No. 2,869,117 granted January 13, 1959. The Doppler radar system il illustrated in FIG. l delivers ground speed as an alternating voltage the frequency of which is proportional to ground speed and delivers the drift angle, es, as three-wire information obtained from a synchro transmitter. The frequency of the ground speed signal is proportional to ground speed and therefore the total accumulated number of cycles is proportional to the distance travelled. The ground speed signal is therefore led to a cycle counter 12 which is arranged to generate a signal after a predetermined number of cycles have been received. The output of the cycle counter 12 may control either the motive power unit 13 of the aircraft or the elevation control surfaces 14 or both.

The three-wire information indicative of the drift angle, et, is led by conductors 15 to the stator of a synchro control transformer 16 the rotor winding 1S of which has a voltage induced therein when the angle ot is different from the angular position of the rotor winding 18, and its shaft 17. This induced voltage constitutes a steering error signal and is passed to an integrator 19, about which more will be said later, and thence to the steering control mechanism 21.

The aircraft is also equipped with a gyroscope Z2 which maintains its spin axis, represented by the shaft 23, at a fixed angular position. rIhe shafts 17 and 23 are connected together by means of a slip clutch 24- so that the angular positions between the two shafts may be adjusted. A handwheel 25 is connected to the shaft 17 so that this adiustment may be made. lf desired the slip clutch may be replaced by a mechanical differential, but at present the slip clutch is preferred because of its simplicity. An indicator Zit is provided to display the angular position of shaft 17 with respect to the longitudinal axis of the aircraft.

ln operation, the gyroscope 22 is started while the aircraft is on the ground and its spin axis may be in any direction such as that represented by the line 31 of FIG. 2. The angle 00 between the spin axis of the gyroscope and the desired course of the aircraft cannot, of course, be controlled accurately, but its value is not important. The

angle 0 between the desired course and the craft axis can, however,`be determined accurately by ground instruments, and the handwheel 25 is adjusted until the position of the shaft i7, as shown by the indicator Ztl, is precisely equal a to this angle 0, which anguiar position will thereafter be maintained by tbe gyroscope 22.

The drift angle a is the angle between the axis of the antenna, represented by the line 32 in iFiG. 2, and the longitudinal axis of the aircraft, represented by the line 33. During flight the Doppler radar system lll` operates to maintain the axis of the antenna precisely along the ground path of the aircraft in the manner previously described briey in this specification and as fully described in the aforementioned copending applications. It can be seen from FIG. 2 that if the aircraft is on the desired course, the angles and et will be equal. It is apparent from FIG. l that since the stator windings of the control transformer llo are excited in accordance with the angle a and since the rotor is positioned in accordance with the angle 9, the rotor winding is will have no voltage induced in it when the angles 9 and a are equal. If these angles differ by less than four degrees, the Voltage induced in winding *1S will be very nearly proportional to 0 1. This voltage is used as an error signal and, after integration by the integrator T19, controls the steering apparatus 2l so as to maintain -a equal to zero. Before the craft is launched, the cycle counter It?. should be adjusted to generate an output signal after a predetermined number of cycles have been counted so that the motive power of the craft may be cut o, or the elevators depressed, or both, so as to bring the craft to the earth at the desired distance from the starting point.

rthe procedure for setting up Vthe apparatus may be summarized as follows. The gyroscope 22 is started; the angle 0 is measured and set into the shaft t7 by means of the hand wheel 25; the cycle counter 12 is adjusted in accordance with the desired distance and then the aircraft is launched. The Doppler radar system .ll and the gyroscope 22 together will keep the aircraft on its course and the cycle counter 12 will return the craft to the earth at the desired distance from its starting point.

lt would be possible to dispense with the integrator 19 of FG. l and operate the steering control mechanism 21 directly from the output of rotor winding 18. However, this procedure would have the disadvantage that if the aircraft' left the desired ground path for any reason, for example, due to wind, the craft would only be returned to the desired course which would be parallel to but laterally displaced from the desired ground path. It is therefore preferred that some apparatus be employed to integrate the error signal.

Referring now to PEG. 3, one form of integrator is shown within the dotted lines 19. The error signal from the winding 1S operates through a rate servo amplifier 36, a motor 37 and a tachometer generator 38 to rotate a shaft 39 at a speed proportional to the error signal. The tachometer generator 38 is a generator whose frequency is constant and whose amplitude is proportional to its speed of rotation. As shown in FIG. 3, the input to the amplifier 36 is the difference between the voltage of winding 13 and the voltage of the generator 38 so that the speed of the shaft 39 is proportional to the voltage from winding t8 and the position of shaft 39 represents the accumulated value of @-a which, in turn, is very nearly equal to the accumulated deviation of the craft from the desired ground path. The shaft 39 adjusts the steering control mechanism 21 to return the aircraft to the desired ground path.

Referring now to FiG. 4, there is shown another form of integrator which may be used. rl`he voltage of the winding la which is an alternating voltage of reversible phase is converted to a direct voltage of reversible polarity by means of a phase detector ri'he output of the phase detector dit is passed through an integrating amplifier 42 which may, for example, comprise a direct coupled Miller Feedback amplifier. The output of the amplifier 42 is therefore a direct voltage indicative of the accumulated deviation of the aircraft from the desired ground path spr/aser a?. and may be used to adjust the steering control mechanism 21.

Referring now to FIG. 5, there is shown the starting point and the target together with the desired ground path connecting them. Let it be assumed that the aircraft has deviated from the desired ground path and is now at some arbitrary point P.

Let it also be assumed that the ground speed vector is making some arbitrary angle -a with the desired ground path. The ground speed vector can be resolved into two components Vgx and Vw parallel and perpendicular respectively to the desired ground path. it can be Seen that, in order to return the craft to the desired ground path and to keep it there, fVgydt must be zero. This is a more accurate steering error signal than Mfr-00dr used in the apparatus so far described, since for accuracy the apparatus of FiGS. l and 4 requires that (-ot) be always small and that the ground speed be constant. It can also be seen that the ground distance from the starting point to the target is jfVgxdt rather than fVgdt used in the embodiment of FGS. l to 4. The errors introduced are smail but may be eliminated by a slight modification of the apparatus.

Referring now to FlG. 6, there is shown the same Doppler radar system l1. The three-wire output indicative of the drift angle or is led by conductors i5 to control transformer 51 which cooperates with a servo amplifier 52 and a motor 53 to position the shaft 54 in accordance with the angle a. The gyroscope 22 is connected as before so that the shaft 17 is positioned in accordance with the angle 0. A mechanical differential 56 subtracts a from 0 delivering its output to a shaft S7 which output is visually displayed on an indicator 5S.

Doppler radar systems suchk as the system 11 are usually provided with several ground speed outputs one of which is in the form of an alternating voltage of constant frequency the magnitude of which is proportional to ground speed and this form of output is used in the embodiment of FIG. 6. lf such an output is not available,- it may be secured by conventional apparatus from the voltage the frequency of which is proportional to ground speed; The ground speed voltage is led by conductors 59 to' a booster amplifier 61 which is provided to prevent loadmg of the radar system 11. The output of the amplifier 61 energizes the rotor winding of an inductive resolver' 63 the rotor of which is positioned by the shaft 57. The' voltages induced in stator windings 64 and 65 will therefore be proportional to Vg sin (f2-cc) and Vg cos (l-a) respectively.

The voltage of winding 64 is led to a rate servo amplier 66 which cooperates with a tachometer generator 6.7 and a motor 68 to rotate a shaft 69 at a speed proportional to Vg sin (-a). The angular position of the shaft 69 is therefore indicative of fVg sin (0-)dt, and is used to adjust the steering control mechanism 21.

The voltage of winding 65 is led to a rate servo arnplitler 71 which cooperates with a tachometer generator 72 and a motor 73 to rotate the shaft '74 at a speed proportlonal to Vg cos (0-a). The angular position of the shaft 74 will therefore be proportional tofVg cos (0-a)dt and may be employed to operate the elevation control mechanism ,te when the desired distance has been traversed. In FIG. 6, this mechanism has been indicated schematically as comprising a gear box 76 and a cam 77 which operates a switch 7S to control the mechanism 14.

The apparatus of FIG. 6 is more accurate than that of FIGS. 1 4 because of the use of the more accurate steering error and distance travelled signals, as previously explained. Greater flexibility is provided by the use of the mechanical differential 56 to subtract from 0, permitting greater instantaneous values of -a without introducing errors.

it can be seen that each of the navigation systems described above secures the high accuracy obtainable with Doppler radar techniques without requiring airborne apparatus for determining true or magnetic north or for computing the desired course. The course is determined by ground based instruments and the airborne gyroscope remembers Athis course and provides continuously a measure of the difference between the desired course and the axis of the aircraft.

The apparatus described is merely illustrative and it will be understood that many modifications may be made within the scope of the invention.

What is claimed is:

l. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, means for determining continuously the magnitude and sense of a first angle equal to the angle between a reference direction on the frame of said aircraft and its ground path, means for determining continuously the magnitude and sense of a second angle equal to the angle between the desired course and said reference direction, means for determining continuously the ground speed of said aircraft, means for generating signals indicative of functions of said ground speed and of the algebraic difference between said first and second angles, and means responsive to said signals for steering said aircraft in the horizontal and vertical planes. i,

2. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, Doppler radar means for determining continuous- 'ly a first angle equal to the angle between the longitudinal axis of said aircraft and its ground path and for deriving continuously a first signal indicative of the ground speed of said aircraft, gyroscopic means for maintaining constant the angular position of a first shaft, means for mechanically joining a second shaft to said first shaft in any selected angular relationship whereby the position of said second shaft may represent a second angle equal to the angle between the desired course and said longitudinal axis, means for deriving a second signal indicative of the algebraic difference between said rst and second angles, and means responsive to said first and second signals for steering said aircraft in the horizontal and vertical planes.

3. Apparatus for guiding an aircraft over a predetermined ground path comprising, means for determining continuously the magnitude and sense of a first angle equal to the angle between a reference direction on the frame of said aircraft and its ground path, means for determining continuously the magnitude and sense of a second angle equal to the angle between the desired course and said reference direction, means for generating a signal indicative of the time integral of the algebraic difference between said first and second angles, and means responsive to said signal .for steering said aircraft.

4. Apparatus for guiding an laircraft over a predetermined ground path comprising, means for determining continuously a first angle equal to the angle between the longitudinal axis of said aircraft and its ground path, gyroscopic means for maintaining constant the angular position of a first shaft, means mechanically joining a second shaft to said first shaft in any selected angular relationship whereby the position of said second shaft may represent `a second angle equal to the angle between the desired course and said longitudinal axis, means for deriving a first signal indicative of the algebraic difference between said first and second angles, means for deriving an error signal indicative of the time integral of said first signal, and means responsive to said error signal for steering said aircraft.

5. Apparatus for guiding an aircraft over a predetermined ground path comprising Doppler radar means for determining continuously a first angle equal to the angle between a reference direction on said aircraft and its ground path, gyroscopic means for maintaining constant the angular position of a first shaft, means for mechanically joining a second shaft to said first shaft in any selected angular relationship whereby the position of said second shaft 4may represent a second angle equal to the angle between the desired course and said reference direction, means for obtaining an error signal indicative of the algebraic difference between said first and second angles, means for integrating said error signal and means responsive to the integral for steering said aircraft.

6. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, means for determining continuously a first angle equal to the angle between a reference direction of said aircraft and its ground path, means for determining continuously a second angle equal to the angle between the desired course and said reference direction, means for determining continuously the ground speed of said aircraft, means for integrating the ground speed to determine the distance travelled, means for generating an error signal indicative of the algebraic difference between said first and second angles, means responsive to said error signal for steering said aircraft and means responsive to a predetermined distance travelled for decreasing the eleva-tion of said aircraft.

7. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, Doppler radar means for determining continuously a first angle equal to the angle between a reference direction on said aircraft and its ground path and for deriving continuously a signal indicative of the ground speed of said aircraft, means for determining continuously a second angle equal to the angle between the desired course and said reference direction, means for obtaining an indication of the algebraic difference between said first and second angles, means responsive to said indication for steering said aircraft in a horizontal plane, means responsive to said derived signal for determining continuously the distance travelled by said aircraft and means responsive to a predetermined distance travelled for decreasing the elevation of said aircraft.

8. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, Doppler radar means for determining continuously a first angle equal to the angle between the longitudinal axis of said aircraft `and its ground path and for deriving continuously a voltage the frequency of which is proportional to the ground speed of said aircraft, gyroscopic means for determining continuously a second angle equal to the angle between the desired course and said axis, synchro means for obtaining an error signal indicative of the algebraic difference between said first and second angles, means for integrating said error signal, means responsive to the integral for steering said aircraft in a horizontal plane, means for counting a predetermined number of cycles of said voltage the frequency of which represents ground speed, and means responsive to the .counting of said predetermined number of cycles for decreasing the elevation of said aircraft.

9. Apparatus for guiding an aircraft over a predetermined ground path for a predetermined distance comprising, Doppler radar means for determining continuously ya first angle equal to the angle between the longitudinal axis of said aircraft and its ground path and for deriving continuously a voltage the frequency of which is proportional to the ground speed of said aircraft, gyroscopic means for maintaining constant the angular position of a first shaft, means for mechanically joining a second shaft to said first shaft in any selected `angular relationship whereby the position of said second shaft may represent a second angle equal to the angle between the desired course and said axis, synchro means for obtaining an error signal indicative of the algebraic difference between said first and second angles, means for integrating said error signal, means responsive to the integral for steering said aircraft in a horizontal plane, means for count- 'ng a predeteri'ninedv number of cyelesof-said voltage the requency of which represents" groundspeed, and means espon'sive to the counting-o-fsaid predetermined number )f cycles for decreasingl the elevation of said aircraft.

10. Apparatus for guiding an aircraft over a predeternined ground path for a` predetermined distance cornnrising, means for determining continuously a rst angle :qual to the angle between a reference direction on said iircraft and its ground path, means for determining con- ,inuously a second angle equal -to the angle between the lesired course and said reference direction, means for ier-iving continuously a signal indicative of the ground speedl of said aircraft, and means jointly responsive to said signal and to the algebraic difference between said rst and second angles for steering said aircraft in the horizontal plane and for controlling the elevation of said aircraft.

1l. Apparatus for guiding anaircraft over a predetermined ground path for a predetermined distance comprising, Doppler radar means for determining continuously a iirst angle equal to the angle between a reference direction on said aircraft and its ground path and for deriving continuously a first signal indicative of the ground speed of said aircraft, gyroscopic means for maintaining constant the angular position of a first shaft, means for mechanically joining a' second shaft to said rirst shaft in any selected angular relationship whereby the position of said second shaft may represent a second angle equal to the angle between the desired course andl said reference direction, means foi-,continuously deriving a second signal indicative of the algebraic difference between said first and second yangles, and means jointly responsive to said first and second signals `for controlling said aircraft in azimuth and elevation. Y

12. Apparatus for guiding an aircraft over a predeter# mined ground path for ak predetermined distance' compris:- ing, oppler radar means for determining continuously a rst angle equalto the angle betweenu the' longitudinal axis of said aircraft and its ground path and for deriving continuously an alternating voltage the magnitude of which is proportional to the groundA speed of said' air- Graft, gyroscopic means for maintaining constant the angular position of afirst` shaft, means for mechanically joining a secon-d shaft to said iirst shaft in any selected angular relationship whereby the position of said second shaft may represent a second angle equal to the angle between the desired course and said axis, means for conY tinuously deriving a representation of a third angle equal to the algebraic diiierence between said iirst and second angles, means jointly responsive to said representation of said third angle and to said alternating voltage for deriving a first signal proportional to the product of the ground speed and the sine `of said thir-d angle and for deriving a second signal proportional to the product of the ground speed and the cosine of said third angle, means for integrating each of said signals with respect `to time, means responsive to the integral of said first signal for steering said aircraft in a horizontal plane, and means responsive to the integral of said second signal for controlling the. elevation of said aircraft.

References Cited in the tiie of this patent UNlTED STATES PATENTS 1,670,641 Sperry May 22, 1928 2,280,117 Crane et al Apr. 21, 1942 2,372,185 Wittkuhns Mar. 27, 1945 2,419,970 Roe et al. May 6, 1947 2,476,032 Feldman July 12, 1949 2,482,869 Thompson Sept. 27, 1949 2,515,248 McCoy July 18, 1950 2,613,350 Kellogg Oct. 7, 1952 2,718,091 Greenwood Sept. 13, 1955 2,745,614 Bennett et al May 15, 1956 2,773,382 Rand Dec. 1l, 1956 2,821,349 Sohn Jan. 28, 1958 2,869,118 Tull Jan. 13, 1959 2,962,244 Harrison Nov. 29, 1960 OTHER REFERENCES An Analysis for Human Flight Control, IRE conven-. tion record, 1956, part 8, pp. 69-83. 

